1. Field of the Invention
The present invention relates to a multilayer film formed body which has a diamondlike carbon film as a surface layer, and is suitable for a surface protection film for a member which especially requires wear resistance and surface smoothness such as a slide member for precision molds, cutting tools, wear resistant machine parts, abrasives, magnetic and optical parts, and printer heads.
2. Description of the Related Art
Hard carbon is a hard material generally called as diamondlike carbon. The diamondlike carbon may be abbreviated as xe2x80x9cDLCxe2x80x9d.
The DLC has an intermediate structure of mixed diamond and graphite. The DLC has high hardness as diamond, and is excellent in wear resistance, solid lubrication, heat conductance, and chemical stability. Thus, it has come to be used as a protective film for different types of parts such as slide members, molds, cutting tools, wear resistant machine parts, abrasives, and magnetic and optical parts.
Physical vapor deposition (PVD) such as sputtering and ion plating, and chemical vapor deposition (CVD) are adopted as a method for forming a DLC film. The DLC film generally generates an extremely large internal stress when the film is formed, while it has high hardness and Young""s modulus, because its deformability is extremely small, it has low adhesiveness to substrate, and has a defect of easily separating.
Thus, different technologies have been proposed for improving adhesiveness to substrate.
They are roughly divided into two categories including:
(1) Controlling film stress, and
(2) Providing an intermediate layer between the substrate and the carbon film.
These technologies have the following problems, and it has been required to improve these problems.
The method in (1) does not essentially solve the problem of instability of the adhesiveness at the heterogeneous interface between the substrate and the carbon film.
The method in (2) essentially uses the film which has an intermediate characteristic between the substrate and the DLC in mechanical property to combine the substrate with the DLC film. A material including a hard brittle material is used for the intermediate layer. However, when CVD or PVD is used to form a thick film with thickness of several micrometers, or a hard film including a large amount of the diamond component whose hardness exceeds 40 Gpa is formed, defective adhesiveness becomes remarkable.
When an iron material is used as the substrate, and a multilayer film which has a DLC film as the outermost layer is formed on the substrate, because the internal stress of the DLC film, which is the outermost layer, is large, the adhesiveness between the intermediate layer and the DLC film is inferior. Especially when the thickness of the highly hard DLC film exceeds 3 xcexcm, it is difficult to secure sufficient adhesiveness.
The iron material is widely used, and has usefulness such as inexpensiveness and excellent toughness compared with carbide. It has been expected to establish a technology for adhesively covering this useful iron material with the DLC film.
The object of the present invention is to use an iron material as a substrate, to form a DLC film as the outermost layer presenting excellent adhesiveness even when formed relatively thickly on the substrate, and to provide a hard multilayer film formed body.
The multilayer film formed body of the present invention comprises an outermost layer comprising a diamondlike carbon film, a substrate comprising an iron material, and an intermediate layer comprising a first layer on the substrate side comprising at least either metal of Cr and Al, and a second layer on the outermost layer side comprising an amorphous layer including carbon and at least either metal of Cr and Al.
It is preferable that the second layer has a gradient structure where the metal decreases as the position becomes close to the outermost layer, and the hardness of the second layer increases stepwise or continuously as the position becomes closer to the outermost layer.
It is preferable that the hardness of the second layer close to the first layer is close to the hardness of the first layer.
It is preferable that the hardness of the second layer close to the outermost layer is close to the hardness of the outermost layer.
It is preferable that a stress relaxation layer comprising carbon is formed between the second layer and the outermost layer. It is more preferable that the hardness of the stress relaxation layer increases stepwise or continuously as the position becomes closer to the outermost layer.
It is preferable that the hardness of the stress relaxation layer at an interface with the second layer is close to the hardness of the second layer. It is preferable that the hardness of the stress relaxation layer close to the outermost layer is close to the hardness of the outermost layer.
It is preferable that a diffusion layer is formed by diffusing the metal elements constituting the first layer on the surface of the substrate.
It is preferable that a mixing layer is formed between the substrate and the first layer, and has mixed elements from the metal elements constituting the first layer, and the elements constituting the substrate.